Patent Application
20250188582
More restrictive exhaust emissions laws for diesel engines have driven changes in engine design including the need for high-pressure electronic fuel injection systems. Engines built according to the new designs use higher combustion pressures, higher operating temperatures and less lubrication than previous designs. Components of the new designs, including valve seat inserts (VSI), have experienced significantly higher wear rates. Exhaust valve seat inserts and valves, for example, must be able to withstand a high number of valve impact events and combustion events with minimal wear (e.g., abrasive, adhesive and corrosive wear). This has motivated a shift in materials selection toward materials that offer improved wear resistance relative to the valve seat insert materials that have traditionally been used by the diesel industry.
Another emerging trend in diesel engine development is the use of EGR (exhaust gas recirculation). With EGR, exhaust gas is routed back into the intake air stream to reduce nitric oxide (NOx) content in exhaust emissions. The use of EGR in diesel engines can raise the operating temperatures of valve seat inserts. Accordingly, there is a need for lower cost exhaust valve seat inserts having good hot hardness for use in diesel engines using EGR.
Also, because exhaust gas contains compounds of nitrogen, sulfur, chlorine, and other elements that potentially can form acids, the need for improved corrosion resistance for alloys used in exhaust valve seat insert applications is increased for diesel engines using EGR. Acid can attack valve seat inserts and valves leading to premature engine failure. Earlier attempts to achieve improved corrosion resistance were pursued through the use of martensitic stainless steels. Though these steels provide good corrosion resistance, conventional martensitic stainless steels do not have adequate wear resistance and hot hardness to meet the requirements for valve seat inserts in modern diesel engines.
Alloy J130 (available from L.E. Jones Company, and described in U.S. Pat. No. 6,702,905) has been widely used for valvetrain component applications due to its high wear resistant performance at elevated temperature and sustainable materials and manufacturing cost compared to conventional valvetrain component alloys such as nickel-based J70, J96 and J100 and cobalt-based alloys J3 and J10. Alloy J130 contains fine solidification substructure that can be quenched and tempered into tempered martensitic structure in intragranular region. The intergranular region is strengthened by borides and precipitation carbides during tempering treatment. Alloy J130 is air quenchable that the process is preferred compared to popular solvent quenching practice from an environmentally friendly process, safety operation, and automation easy considerations. However, despite the improvements in materials performance to date, there is still need for high performance materials having improved compressive yield strength at elevated temperatures.
In an embodiment, an iron-based alloy having a martensitic microstructure including primary and secondary carbides comprises, in weight percent (wt. %): about 0.005 to 0.5% boron; about 1.2 to 1.8% carbon; about 0.7 to 1.5% vanadium; about 7 to 11% chromium; about 1 to 3.5% niobium; about 6 to 11% molybdenum; about 3 to 10% nickel; and balance including about 60 to 80% iron and incidental impurities.
According to various options, (a) the alloy is tungsten-free, the nickel content is about 4 to 9% and the iron content is about 60 to 80%, (b) the alloy includes up to about 1.6% Si and/or up to about 2% Mn, (c) the boron content is about 0.1 to 0.3% and the iron content is about 60 to 70%; (d) the carbon content is about 1.4 to 1.8% and the nickel content is about 4 to 8%; (e) the vanadium content is about 0.8 to 1%; (f) the chromium content is about 9 to 11%; (g) the niobium content is about 1 to 2.5%; (h) the molybdenum content is about 8 to 10%; (i) the alloy includes up to about 4% cobalt; (j) the alloy includes about 1.5 to 2.5% cobalt; (k) copper is substituted partially or completely for cobalt; (1) the contents, in weight percent, of the boron, vanadium and niobium are represented by B, V and Nb, respectively, and satisfy the following condition: 1.9%<(B+V+Nb)<4.3%; (m) the alloy is in a hardened and tempered condition; (n) the primary carbides have a width smaller than about 10 microns and the secondary carbides are smaller than about 1 micron; (o) the alloy is in the form of a casting; (p) the alloy is in a hardened and tempered condition having a hardness of at least about 42 Rockwell C; (q) the alloy is in a hardened and tempered condition and exhibits a Vickers hot hardness at a temperature of 800° F. of at least about 475; (r) the alloy is in a hardened and tempered condition and exhibits a high temperature compressive yield strength at 800° F. of at least about 190 ksi; and/or (s) the alloy exhibits a dimensional stability of less than about 0.5×10-3 inches after 20 hours at 1200° F.
In an embodiment, a part for an internal combustion engine comprises the iron-based alloy described above optionally in the form of a casting, pressed and sintered compact, coating or part such as a ball bearing. For example, the part can be a valve seat insert for an engine such as a diesel engine optionally using EGR.
In the following discussion, the J130 alloy system is investigated with a goal of achieving higher hardenability for wear resistant related applications. This idea is supported by fundamental metallurgical principles that a stabilized austenite stage prior to a quenching process benefits consistency of quenching result. It is also based upon the basic metallurgy of austenitic stainless steels that martensite will not form when the nickel content reaches to a certain level. Hence, in the following discussion, nickel additions are evaluated from both a hardness/strength and toughness enhancement aspect. An alloy system with enhanced wear resistance can make a significant contribution to performance of valvetrain designs in internal combustion (“IC”) engine applications including methanol and hydrogen fueled IC engines.
In the following discussion, the effect of nickel content on air quenchability is evaluated over a Ni range of no nickel (Ni) addition to 12.5 wt. % Ni addition. All of the samples evaluated were cast with a 150 lb induction melting furnace with proper raw materials furnace charging. Two reference J130 heats (7B15G and 3B24XA), one reference J120V heat, and one reference J160 heat were made with a 750 lb induction melting furnace according to standard alloy production methods. The J130, J120V, and J160 sample heats used for hardenability assessment are summarized in Table 1.
Heat treatment of the samples was carried out using heat treatment furnaces at the L.E. Jones (“LEJ”) Casting Prototype Center for hardening and tempering treatments. Each sample was enclosed in a stainless steel envelope prior to being placed in the heat treatment ovens.
All the heats were analyzed using LEJ Spectrometer units with respective alloy analysis method and reference type standard. It can be noted that in addition to the differences in Ni content, there is a small variation in the remaining alloying elements incidental to the experimental procedure. The effect of Ni on the air quench-ability of the samples was investigated per the idea that nickel can lower the eutectoid reaction temperature and reduce the percentage of intercellular region in the J130 alloy system.
Another concept under investigation is the potential formation of Fe3Ni, FeNi2, and FeNi3 in the J130 alloy system when the alloy system has an adequate nickel content. Hence, the following discussion examines a range of nickel content from 0.09 wt. % (incidental) through 12.0 wt %. Among these heats, Heats 7B15G, 9K12M, and 3B24Q are with standard J130 alloy composition adopted for a comparative evaluation purpose.
The latent heat measurement was performed using six heats from the Experiments and References listed in Table 1. The measurements were carried out utilizing a standard LEJ thermocouple set built for latent heat measurement application along with the standard LEJ latent heat measurement procedure. The results of latent heat measurement are exhibited in
The latent heat measurement results applying temperature-time elapse results manifested that two major phase-transformations took place for all the Experiments and Reference samples evaluated from liquid state (>1400° C.) to 1000° C. including bulk liquid to solid (1283° C.˜1306° C.) and solid-state phase transformations in a temperature range between 1115° C. and 1150° C. It was also likely a hint of liquid to solid phase formation within a temperature range between 1375° C. and 1389° C. that was most likely related to peritectic reaction resulting in a ferrite formation in liquid metal. As a result, Heat 3B17A (4.95 wt. % Ni) displayed the highest melting temperature at approximate 1306° C. while Heat 3B02XA (7.63 wt. % Ni) displayed the lowest melting temperature at approximate 1299° C. followed by Heat 3B16XA (2.56 wt. % Ni) at approximate among the heats evaluated. A summary of the melting measurement results is tabulated in Table 2.
The time between major liquid to solid (1285° ˜1305° C.) and solid to solid phase transformation was measured for the six heats adopted for the latent heat investigation with the results shown in
The effect of nickel content on temper response was evaluated with seven different heats from 25° C. through 900° C. and a total of three hours thermal soaking was applied for all the tests. The samples used for this temper response investigation were in a ring shape with dimensions of 1.935″ OD, 1.750″ ID, and 0.3050″ height. Radial crush tests were conducted by pressing on the OD surface applying a tensile tester until the sample was ruptured.
The Experiment with Heat 3B02XB which had 7.63 wt. % Ni exhibited a small bulk phase transformation. The Experiment displayed somewhat lower bulk hardness compared to the other four Experiments with lower nickel content except when temperature reached to approximately 593° C. Within the temperature range between 593° C. to 816° C., Experiment Heat 3B02XB possessed greater bulk hardness than those Experiments having lower nickel content.
The remaining four Experiments and Reference all showed a significant bulk phase transformation within the thermal treatment. For Experiment 3A23XA and Reference, bulk hardness lowered sharply and continuously starting at approximate 550° C. Experiments 3A25XA (4.08 wt. % Ni), 3A25XB (4.88 wt. % Ni), and 3B16XA (2.56 wt. % Ni) along with Reference (slightly) exhibited a “U” bulk hardness curve in the tempering temperature range between 550° C. and 825° C. likely due to rehardening when the thermal treatment temperature was above approximately 760° C.
Considering both bulk hardness response and radial crush response shown in
Air quench-ability analysis was carried out using the air quench-ability test method developed at LEJ. The test specimen is with a dimension of 3.5″ long and 1.0″ in diameter cylinder in as-cast condition. The sample is placed in laboratory oven for one hour thermal soaking at 850° C. then followed by a test end quench with compressed air for five minutes. The compressed air is applied on the quench end of the cylinder samples with at 5.6 m/s flow rate. The bulk hardness measurements were carried out from quenching end to opposite end with a small flat area prepared on the OD surface adopting water cooled grinding process.
A standard LEJ Plint test method was applied for the wear resistance evaluation and the test procedures include 100,000 duration cycles, 20 N applied load, 1.0 mm reciprocating distance, 20 Hz reciprocating frequency, and non-lubrication test condition.
Samples made with five experimental heats i.e., 3B17XA, 3B03XA, 3B16XA, 3B07XA, and 3B10XA were adopted for the compressive yield strength evaluation. These experimental heats varied in nickel content in order to investigate nickel effect on the mechanical property of the alloy system. Table 3 summarizes the compression test results in which Heat 1 is 3B17XA, Heat 2 is 3B03XA, Heat 3 is 3B16XA, Heat 4 is 3B07XA and Heat 5 is 3B10XA in Table 1.
From the CYS test data, it can be observed that for Ni contents of 4 to 8 wt. % Ni, the samples exhibited compressive yield strengths of over 170 ksi at temperatures ranging from ambient to 900° F. compared to samples with lower and higher Ni contents which had a maximum of 114 ksi (2.56 wt. % Ni) and 98.5 ksi (10.62 wt. % Ni) over the temperature range of ambient to 900° F. The CYS test data shows that there is an unexpected increase in compressive yield strength for J130 alloys with increased Ni contents in the range of about 3-10 wt. % Ni, preferably about 4-9 wt. % Ni and most preferable about 4-8 wt. % Ni. Accordingly, for iron base alloys with about 0.005 to 0.5 wt. % B, about 1.2 to 1.8 wt. % C, about 0.7 to 1.5 wt. % V, about 7 to 11 wt. % Cr, about 1 to 3.5 wt. % Nb, about 6 to 11 wt. % Mo, balance about 60 to 80 wt. % Fe and incidental impurities, the alloy can include 3 to 4 wt. % Ni, 4 to 5 wt. % Ni, 5 to 6 wt. % Ni, 6 to 7 wt. % Ni, 7 to 8 wt. % Ni, 8 to 9 wt. % Ni or 9 to 10 wt. % Ni. A preferred alloy includes about 0.005 to 0.5 wt. % B, about 1.2 to 1.8 wt. % C, about 0.7 to 1.5 wt. % V, about 7 to 11 wt. % Cr, about 1 to 3.5 wt. % Nb, about 6 to 11 wt. % Mo, about 4 to 8 wt. % Ni, and balance about 60 to 70 wt. % Fe and incidental impurities.
Wear resistance of wear and heat resistant alloys was related to hardness and toughness hence microstructure of an alloy. As discussed herein, by modifying a standard J130 alloy to include higher Ni contents, the quench-ability can substantially improved with the added benefit of enhanced bulk hardness, enhanced toughness and significantly improved compressive yield stress properties. In general, higher bulk hardness corresponds to better wear resistance. One of the optimal nickel contents or narrow nickel content range was detected through this investigation with which an enhanced J130 alloy system displayed the highest air quench-ability. The new alloy, J130M with about 3 to 10% Ni, preferably about 4 to 9% Ni and more preferably about 4 to 8% Ni, possessed a sound and sustained bulk hardness, toughness and improved compressive yield stress from ambient through elevated temperature (>800° C.).
The operating temperatures for common valve train intake applications is 50 to 350° C. (260 to 660° F.) and for common valve train exhaust applications is 300 to 600° C. (570 to 1110° F.).
In the past, J130 has been mostly applied for exhaust applications and more recently, J130 has been tested in a couple of diesel engine platforms for intake application. With the improved properties due to the increase in Ni content, J130M is anticipated to be a good candidate for both intake and exhaust applications.
Although the present invention has been described in connection with preferred embodiments thereof, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made without departing from the spirit and scope of the invention as defined in the appended claims.
