US2883281A - Air hardening graphitic steel - Google Patents

Description

United States Patent ,0

AIR HARDENING GRAPHITIC STEEL No Drawing. Application December 6, 1957 Serial No. 700,982

3 Claims. (Cl. 75-123) This invention relates to graphitic steels of high hardenability and of controlled graphitic carbon content. The term high hardenability as used herein refers to the ability of the steel to be hardened in still air from an austenitizing temperature to a minimum hardness of Rockwell C 58 (Re) throughout relatively heavy sections.

Graphitic steels are well known and they have been widely used. They are characterized by containing free graphite and they possess the ability to develop high hardness, good machining properties, resistance to wear, and desirable mechanical properties. This combination of properties adapts those steels particularly for use as dies of a wide variety of uses, and as punches, breaches, spinning rolls, and other tools for related uses.

Most of the known graphitic steels are hardened by liquid quenching. An air hardening type has been proposed but experience has shown that although it possesses good graphitizing properties it is not capable of commercial exploitation in sections greater than about 1 /2 inches. In contrast, conventional air hardening steels, e.g., the standard SCr-lMo, the 12Cr-1.5C steels,

ability properties that characterize the invention and do not interfere with development of desired graphite levels brought about in the manner now to be described. Thus, the steels may contain tungsten which, in principle, behaves similarly to molybdenum, as well as small amounts of vanadium (up to 0.5 percent) which, in principle, behaves similarly to chromium and also acts as a grain refiner. p

In the practice of the invention the steels are melted, hot worked, and annealed to eflfect graphitization all in accordance with standard graphitic steel practice, care being taken to avoid graphite formation in the ingots and during hot working. The steels should be hardened by cooling in air from within the range of about 1450" to 1550 F., the lower temperature being applicable to small sections, say up to one and one-half inch dimension, and the temperature being progressively increased toward the upper value as the section size increases, e.g., using 1525 F. at five and one-half inch and greater sections. These low hardening temperatures are advantageous in that they are 200 to 300 F. below those necessary for most competitive non-graphitic air hardening steels. This confers low distortion, low decarburization, and low retained austenite.

The annealed hardness, in which condition these steels are commonly sold to the trade, will normally range and some high manganese types, can be air hardened to Rc 60 at the centers of rounds as great as 4 inches, 5 inches and 6 inches in diameter respectively.

It is among the objects of this invention to provide graphitic steels capable of being hardened in air to a minimum of about Re 58, and preferably of at least about Re 60, up to the center of sections as large as six-inch rounds and equivalent non-circular sections; that may be produced and processed easily according to standard graphitic steel practice; that possess good machinability; that gave dimensional stability comparable to that of competitive non-graphitic steels; and that may be hardened at comparatively low temperatures,

A further object is to provide steels in accordance with the foregoing objects containing from about'0.2 to 0.6 percent of graphitic carbon that is substantially uniformly dispersed throughout the section.

Other objects will be apparent from the following specification.

I have discovered, and it is upon this that the invention is largely predicated, that the objects of the inven tion are attained with steels containing from about 1 to 2 percent of carbon, not over about 0.2 percent of chromium, from about 1.7 to 2.5 percent of manganese, from about 1.3 to 1.75 percent of molybdenum, from about 1 to 2.5 percent of nickel, and from about 1 to 1.5 percent of silicon. Preferably the steels contain about 1.35 percent of carbon, less than about 0.15 percent of chromium, about 1.85 percent of manganese, from about 1.4 to 1.6 pcrcent of molybdenum, from about 1.8 to 1.9

The steels may contain phosphorus and sulfur in amounts found in graphitic steels.

Apart from the foregoing alloying constituents, the

remainder of the steels is iron together withimpurities and elements that do not adversely afiect'the hardenv percent of nickel, and from about 1.15 to 1.25 percent 'of silicon.

from about 235 to 275 Brinell, according to the graphite level. In tempering, as to relieve stress or for rehardening, care should be taken to keep the temperature below that at which re-solution occurs. p

These steels have good machinability. They machine with short, discontinuous chips characteristic of other graphitic steels. They possess excellent tempering characteristics.

As air hardened these new steels possess a microstructure of spheroidized carbides uniformly distributed in a high strength matrix through Which there are also uniformly distributed particles of graphitic carbon. In general, with sections up to 3 inches the hardness to be expected is 62-64 Rc, and with larger sections 60-63 Rc, which hardness is substantially uniform across the section.-

The following examples are characteristic of the-steels of this invention. Each of them was made in a 40-ton electric furnace and the heats were poured into 20-inch square ingot molds to produce ingots of 5150 pounds weight. The ingots were charged into a furnace at 1200 F. and cooled slowly to 200 F. after which they were reheated to 1925 F. and hot worked to shapes of various sections and sizes. The hot worked products were then given the following preliminary and final annealing cycles: a

e. in furnace at 10 Samples of the annealed stock having a length 2 /2 times the diameter were turned from larger section sizes and hardened in still air. Analyses, graphitic carbon Patented Apr. 21, 1 959 contents, hardnesses and tempering data are given for each steel.

Example 1 This steel had the following analysis:

This heat was forged to 5", 5 /2", 7%, 8% and 9" rounds.

The annealed product showed the following graphite contents:

Section size- Graphite, percent 5" round .39 7%" round .42 8%" round .39 9" round .45

Hardening as described above gave the following results;

Re Hardness At- Surface Quarter Center 4" Bound Hardened From 1,475" F 62. 8 62.0 61. 6 4 Round Hardened From 1.525 F 62. 5 62.0 61. 7 6" Round Hardened From 1,475 E. 61. 60. 0 59. 8 6" Round Hardened From 1,525 F-.. 61. 60. 3 60. 5

Two inch square samples were cut from a 7%" round in the as-annealed condition. The two inch square samples were then hardened from 1450 F. and tempered for two hours at the temperatures indicated. The data follow:

Example 2 This heat was likewise forged to produce various sizes of rounds and squares. Its analysis was:

0 M11 P S Si Or N1 M0 The annealed product showed the following graphite contents:

Section size-- Graphite, percent 6%" round .46 7" round .57 8" round .61 9" round .56 10 round .54 11" round .49 6" square .50 8" square .51

10" square .47

Hardening as described above gave the following results:

Re Hardness At- Surface Quarter Center 6" Round Hardened From 1,525 F. 60.8 60.7 60. 8 7 Round Hardened From 1,525 F..." 58. 8 59. 5 58. 7

Two inch square samples were cut from a 7" round in the as-annealed condition. The two inch square samples were then hardened from 1450 F. and tempered for two hours at temperatures indicated.

Tempering temperature, F.-- Rc hardness As-quenched 61.5 200 61.0 300 61.0 400 59.5 500 59.0 600 58.0 700 -1 55.4 800 53.0 900 51.5 1000 46.0 1100 38.5 1200 32.5

Example 3 In this case the ingots were forged and rolled to produce rounds and flats of varying sizes such as 4" and 6" forged rounds and rolled flats varying from 1%" x 3" to 4" x 9". This heat had the following analysis:

C Mn P 8 N1 M0 Typical graphite contents of the annealed products were:

Section size- 4" round 6" round .21

Hardening as described above gave the following results:

Graphite, percent .45

Re Hardness At;-

Surface Quarter Center 4" Round Hardened From 1,475 F 4" Round Hardened From 1,525 F 6" Round Hardened From 1.475 F 6 Round Hardened From 1,525 F Two inch square samples were cut from a 6 inch square in the as-annealed condition. The two inch square samples were then hardened from 1450 F. and tempered for two hours at temperatures indicated.

Tempering temperature, F.- Rc hardness As-quenched 62.0 200 63.0 300 60.5 400 60.0 500 59.5 600 58.5 700 57.2 800 54.0 900 52.0 1000 47.5 1100 40.0 1200 34.5

From the foregoing data, typical of the invention it will be observed that the desired hardness and graphite levels as well as uniformity of hardness across the section are attained. The data show, furthermore, that the steels are satisfactorily resistant to tempering.

According to the provisions of the patent statutes, I have explained the principle of my invention and have described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

I claim:

1. A hot worked and heat treated article of manufacture formed from steel containing about 1 to 2 percent of carbon, not over about 0.2 percent of chromium, about 1.7 to 2.5 percent of manganese, about 1.3 to 1.75 percent of molybdenum, about 1 to 2.5 percent of nickel, about 1 to 1.5 percent of silicon, and the remainder iron together with elements and impurities in amounts that do not adversely affect the hardening and graphitizing properties, said article having spheroidized carbides and at least about 0.2 percent of graphitic carbon substantially uniformly distributed throughout its section, and having a hardness of at least Rockwell C 58 throughout sections at least as great as six inches diameter resulting from cooling in air from an austenitizing temperature.

2. A hot worked and heat treated article of manufacture according to claim 1 containing about 1.35 percent of carbon, less than about 0.15 percent of chromium, about 1.85 percent of manganese, about 1.4 to 1.6 percent of molybdenum, about 1.8 to 1.9 percent of nickel, and about 1.15 to 1.25 percent of silicon.

3. Steel containing about 1.35 percent of carbon, less than about 0.15 percent of chromium, about 1.85 percent of manganese, about 1.4 to 1.6 percent of molybdenum, about 1.8 to 1.9 percent of nickel, and about 1.15 to 1.25 percent of silicon, and the remainder iron together with elements and impurities in amounts that do not adversely affect the hardenability and graphitizing properties, said steel being characterized by capability of being hot worked and upon cooling in air from an austenitizing temperature of producing structures of spheroidized carbides with at least about 0.2 percent of graphitic carbon substantially uniformly distributed throughout its section, and having a hardness of at least Rockwell C 58 throughout sections at least as great as six inches diameter.

References Cited in the file of this patent UNITED STATES PATENTS 1,910,034 Mitchell et al. May 23, 1933 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,883,281 April 21, 1959 Chester F. Jatczak It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 18, in the table, second column thereof, opposite "300, I

Signed and sealed this: 30th day of June 1959.

(SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Attesting Ofliccr Commissioner of Patents

Claims (1)

1. 3. STEEL CONTAINING ABOUT 1.35 PERCENT OF CARBON, LESS THAN ABOUT 0.15 PERCENT OF CHROMIUM, ABOUT 1.85 PERCENT OF MANGANESE, ABOUT 1.4 TO 1.6 PERCENT OF MOLYBDENUM, ABOUT 1.8 TO 1.9 PERCENT OF NICKEL, AND ABOUT 1.15 TO 1.25 PERCENT OF SILICON, AND THE REMAINDER IRON TOGETHER WITH ELEMENTS AND IMPURITIES IN AMOUNTS THAT DO NOT ADVERSELY AFFECT THE HARDENABILITY AND GRAPHITIZING PROPERTIES, SAID STEEL BEING CHARACTERIZED BY CAPABILITY OF BEING HOT WORKED AND UPON COOLING IN AIR FROM AN AUSTENITIZING TEMPERATURE OF PRODUCING STRUCTURES OF SPHEROIDIZED CARBIDES WITH AT LEAST ABOUT 0.2 PERCENT OF GRAPHITIC CARBON SUBSTANTIALLY UNIFORMLY DISTRIBUTED THROUGHOUT ITS SECTION, AND HAVING A HARDNESS OF AT LEAST ROCKWELL C 58 THROUGHOUT SECTION AT LEAST AS GREAT AS SIX INCHES DIAMETER.