US2914401A - Alloy steel - Google Patents

Description

United States Patent ALLOY STEEL Peter Payson, Pittsburgh, Pa., assignor to Crucible Steel Company of America, Pittsburgh, Pa., a corporation of New Jersey No Drawing. Application February 24, 1958 Serial No. 716,856

3 Claims. (Cl. 75-126) This invention relates to a low alloy steel suitable for the manufacture of hardened bars and, more particularly, to a low cost alloy steel which can be air cooled from an austenitizing temperature to form martensite.

Although not limited thereto the present invention is particularly adapted for use in the manufacture of homogeneous jail bars. As the name implies, homogeneous jail bars are those composed of a solid metal mass having the same composition throughout. resist shattering by a blow or bending stress and must resist cutting with a hacksaw. Furthermore, the bars should be simple toheat treat and should be kept straight during the heat treating operation.

According to the prior art, homogenous jail bars were manufactured from a simple carbon AISI 1060 steel of approximately 0.55% carbon and 0.70% manganese. In order to harden a steel of this type to resist cutting, it must be water quenched from the range of 1500 to 1550 F. The quenching process produces hard martensite on the outside of the bar to resist cutting and relatively ductile pearlite on the inside which gives high resistance to bending stresses. As a consequence of the Such bars must.

water quench, however, the bars may warp or twist. At- I tempts have been made to maintain the bars straight during the quenching operation by securing them in a rigid fixture. This procedure, however, is unsatisfactory since the bars may fracture due to their inability to expand in the fixture. Anothermethod heretofore used was to quench the bars to a temperature of about 500 F., at which point they were straightened in a press. The difficulty with this latter method is that if the bars have hardened before straightening they will fracture in the press as they do in the fixture. Thus, no satisfactory means has heretofore been employed to maintain the bars straight during the quenching process.

As will become apparent from the following detailed description, I have found that an alloy can be prepared which may be air hardened whereby the difiiculty of maintaining the straightness of elongated members in the hardening operation is minimized. Specifically, my alloy consists of a medium carbon steel having relatively small amounts of manganese, silicon, chromium, and molybdenum added thereto. By proper control and adjustment of this composition and by air hardening from the austenitizing temperature range of 1600" F. to 1750 F., I can provide steel bars relatively free from residual stresses having a hard outer surface in the range of Rockwell C 63 to 65. Microanalysis will reveal that with this alloy the bar is martensitic after air cooling. In addition to minimizing straightening difficulties during cooling, the alloy also has high resistance to softening during tempering and has greatly improved toughness characteristics over water quench bars formed from A181 1060 steel; however, the amounts and types of alloying constituents added to my composition are such that the overall cost of the final product is not materially increased over the AISI 1060 bars.

, 2,914,401 Patented Nov. 24, 1959 In accordance with my invention, I provide bar steel of the following broad" and preferred compositions:

ANALYSIS, PERCENT BY WEIGHT Broad Preferred C 55/. 60/. 70 Mn 70/1. 50 .90/1. 20 Si 1. 2012.00 1. 40/1. Cr. 1.00/2. 50 1. 30/1. M0 50/1. 20 60/1. 00

Steels in the foregoing range of composition have a minimum Rockwell C hardness of 63 when air hard-- ened from a temperature of 1700 F. They can be tempered by holding at temperatures from about 200 F. to 300 F. for one hour or longer followed by an air cool while retaining a minimum Rockwell C. hardness of 63. Furthermore, they have good hot workability and should not present difficulties in rolling.

Properties of my new and improved steel are established by the following: Eight 30 pound induction heats, having the analyses given in Table I, were heated to 1975 F. and forged into 1% inch bars, the bars being subsequently stress relieved at 1350 F.

Table I Grade 0 Mn P S Si Ni Or M0 0. 57 1. 00 0. 005 0. 027 l. 17 0. 09 1. 73 0. 76 0. 58 0. 88 0. 005 0. 026 1. 25 0. 09 2. O2 0. 76 0. 65 l. 03 0. 005 0. 027 1. 82 0. 09 1. 64 0. 76 0. 62 1. 78 0. 006 0. 027 1. 94 0. 09 1. 61 0. 76 0 70 1.02 0. 007 0.028 1. 23 0. 09 1. 64 0. 76 0. 72 1. 68 0. 007 0. 027 1. 20 0. 09 1. 49 0. 76 O. 72 1. 13 0. 006 0.026 1. 77 0. 09 1. 74 0. 76 0. 72 l. 76 0. 006 0. 027 1. 77 0. 09 1. 91 0. 76

Ater the bars were stress relieved, five specimens (each /5 inch thick by 1% inch and 1% inch) were cut from each bar and heated to austenitizing temperatures ranging between 1450 F. and 1750 F. for one hour as shown in Table II. Thereafter, each specimen was air cooled to room temperature in still air.

Table H Rockwell G"'Hardness After Air Cooling from a -Austenitizing Treatments 1 Grade 1,450 F. 1,650 F. 1,650 F. 1,700 F. 1,750 F. I

1 Austenitlzing treatment consisted of heating a specimen for one hour at each of the indicated temperatures.

It can be seen from Table II that as the austenitizing temperature increases from 1450 F. to 1700 F., the Rockwell C increases progressively. Above 1700 F., however, the Rockwell C hardness drops off after .the specimen is air cooled. The microstructures of various steels in Table II show that they consist essentially of martensite after being austenitized from about 1600 F. or higher and air cooled. It is apparent that with the composition of the present invention, substantially no high temperature transformation from austenite to pearlite occurs when the alloy is heated above the 1600 F. point.

Table III shows the results of tempering specimens C,

E and F after being air hardened from 1650" F.

3 Table III Rockwell "C Hardness After Tempering 1 Belore tempering, the specimens were austenitized at 1,650 F. for one hour and air cooled. They were then tempered cumulatively for one hour at each of the indicated temperatures and aucooled.

It can be seen from this table that the Rockwell C hardness is substantially unimpaired when the metal is heated to 200 F. for one hour and allowed to air cool. As the tempering temperature progressively increases from 200 F. to 300 F., the Rockwell C hardness decreases but not to any appreciable extent.

The results of deflection tests on three of the steels of Table I are compared with AISI 1060 steel, a composite jail bar and a homogeneous induction hardened steel bar in Table IV. Two specimens, 14 inches in length, of each of the grades C, E and F were machined to 1% inch diameters and heated to 1625 F. and 1675 F., respectively, and cooled in air.

1 The specimen (14 inches long and 1% inches in diameter) was cooled in still air after being austenitized at given temperature.

1 Hardness readings were taken on the broken test piece after grinding two surfaces mutually parallel to the longitudinal axis of the specimen.

Specimen was 14 inches long and 154 inches in diameter.

The regular composite bar of Table IV consists of an austenitic steel matrix provided with high carbon tool steel inserts. With this particular construction, the austenitic steel matrix gives resistance to shattering by blow or bending stresses while the high carbon tool steel inserts prevent cutting with a hacksaw. The homogeneous induction-hardened bar consists of AISI 1060 steel having only its outer surface heated to an austenitizing temperature in an induction coil before quenching. The entirety of the AISI 1060 bar was, of course, heated to an austenitizing temperature and then quenched. It can be seen that the steels of the present invention have a much higher resistance to bending stresses than the steels used in the prior art. Specifically, the resistance to bending stresses in specimen C is almost four times higher than that of a regular composite steel bar and about twice as high as the regular AISI 1060 steel and the homogeneous induction hardened steel.

It can thus be seen that I have provided an air hardenable jail bar having a high hardness and high resistance to bending stresses after being air cooled from an austenitizing temperature. Although I have specifically described the invention in connection with jail bars, it should readily be understood that the steel is equally applicable for other wear resistant articles such as dies, gages, shear blades, cutter bars for lawn mowers and the like, chuck jaws, cams, boring tools, clinker bars, and generally such tools as have considerable length in proportion to diameter and are, therefore, difiicult to maintain straight when they are hardened by a water or oil quench.

I claim as my invention:

1. An alloy steel consisting essentially of about .60 to .70% carbon, .90 to 1.20% manganese, 1.40 to 1.80% silicon, 1.30 to 1.90% chromium, .60 to 1.00% molybdenum and the remainder iron with the usual impurities, characterized in being hardened to a minimum of Rockwell C 63 by air cooling from an austenitizing temperature.

2. An elongated steel article of manufacture having a length many times greater than its longest cross sectional dimension and comprising about: .60 to .70% carbon, .90 to 1.20% manganese, 1.40 to 1.80% silicon, 1.30 to 1.90% chromium, .60 to 1.00% molybdenum, and the rest iron with the usual impurities, characterized in being hardened to a minimum of about Rockwell C" 63 by air cooling from an austenitizing temperature.

3. A jail bar consisting essentially of about .60 to .70% carbon, about .90 to 1.20% manganese, about 1.40 to 1.80% silicon, about 1.30 to 1.90% chromium, about .60 to 1.00% molybdenum, and the remainder iron with the usual impurities, characterized in being hardened in sections up to about 1 /2 inches in diameter to a minimum of about Rockwell C 63 by maintaining the same within the approximate temperature range of 1600 to 1700 F. for about one hour and thereafter air cooling.

References Cited in the file of this patent FOREIGN PATENTS 517,118 Great Britain Jan. 22, 1940

Claims (1)

1. 3. A JAIL BAR CONSISTING ESSENTIALLY OF ABOUT .60 TO .70% CARBON, ABOAUT .90 TO 1.20% MANGANESE, ABOUT 1.40 TO 1.80% SILICON ABOUT 1.30 TO 1.90% CHROMIUM, ABOUT .60 TO 100% MOLYBDENUM,A ND THE REMAINDER IRON WITH THE USUAL IMPRURITIES, CHARACTERIZED IN BEING HARDENED IN SECTIONS UP TO ABOUT 11/2 INCHES IN DIAMETER TO A MINIMUM OF ABOUT ROCKWELL "C" 63 BY MAINTAINING THE SAME WITHIN THE APPROXIMATE TEMPERATURE RANGE OF 1600 TO 1700*F. FOR ABOUT ONE HOUR AND THEREAFTER AIR COOLING.