# US 11,028,457 B2 · Method of heat treating a fastening member

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- Number: US 11,028,457 B2
- Document ID: US11028457B2
- Status: Granted
- Kind: B2
- Application number: 15/651,089
- Filed: 2017-07-17
- Published: 2019-01-17
- Granted: 2021-06-08
- Earliest claimed: 2017-07-17
- Assignees: Caterpillar Inc.
- Applicants: Caterpillar Inc.
- Inventors: Tianjun Liu
- Web page: https://patentgrep.com/patent/US11028457B2

## CPC

- C21D 9/0093: {for screws; for bolts}
- C21D 1/10: by electric induction
- C21D 1/18: Hardening (C21D1/02 takes precedence); Quenching with or without subsequent tempering (quenching devices C21D1/62)
- C21D 1/25: Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
- C21D 1/60: Aqueous agents
- C21D 1/785: {Thermocycling}
- C21D 1/42: Induction heating
- C21D 1/58: Oils
- C21D 2221/00: Treating localised areas of an article
- Y02P 10/25: Process efficiency
- C21D: MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING (surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by this subclass C23F17/00; unidirectional solidification of eutectic materials or unidirectional demixing of eutectoid materials C30B)
- Y02P: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS

## Abstract

A method of heat treating a fastening member having a head portion, a shank portion, and a thread portion includes hardening the fastening member to a first hardness value. Hardening of the fastening member includes heating the fastening member at a first pre-set temperature value. The method also includes tempering the fastening member at a second pre-set temperature value to a second hardness value. The method further includes induction tempering the thread portion of the fastening member. Induction tempering of the thread portion includes heating the thread portion at a third pre-set temperature value to a third hardness value. The third hardness value of the thread portion is less than the second hardness value of the head portion and the shank portion.

## Claims

### Claim 1

A fastening member comprising:
a head portion having an outside head surface and an inside head surface; and
a body portion attached to the head portion, wherein the body portion includes:
a shank portion extending from the head portion, wherein the head portion and the shank portion are tempered to a hardness value between 48 Rockwell C and 60 Rockwell C; and
a thread portion having a plurality of threads, wherein the thread portion is induction tempered to a hardness value between 25 Rockwell C and 44 Rockwell C;
the shank portion originating at the inside head surface and terminating at the thread portion, and being unthreaded along a full shank portion length extending from the inside head surface to the thread portion; and
the thread portion originating at the shank portion and terminating at a fastening member terminal tip, and the plurality of threads are hardened to the hardness value between 25 Rockwell C and 44 Rockwell C along a full thread portion length extending from the shank portion to the fastening member terminal tip.

### Claim 2 (depends on 1)

The fastening member of claim 1, wherein the hardness value of the head portion and the shank portion is about 55 Rockwell C.

### Claim 3 (depends on 1)

The fastening member of claim 1, wherein the thread portion is induction tempered to a depth below the plurality of threads.

### Claim 4 (depends on 1)

The fastening member of claim 1, wherein the fastening member is hardened at a first pre-set temperature value prior to tempering, hardening of the fastening member including heating the fastening member.

### Claim 5 (depends on 4)

The fastening member of claim 4, wherein the first pre-set temperature value lies between 800° C. and 950° C.

### Claim 6 (depends on 4)

The fastening member of claim 4, wherein the fastening member is quenched using a fluid medium upon heating the fastening member at the first pre-set temperature value, wherein the fluid medium is selected based on a material of the fastening member.

### Claim 7 (depends on 6)

The fastening member of claim 6, wherein the fastening member is tempered at a second pre-set temperature value upon the quenching of the fastening member.

### Claim 8 (depends on 7)

The fastening member of claim 7, wherein the second pre-set temperature value lies between 150° C. and 300° C.

### Claim 9 (depends on 1)

The fastening member of claim 1, wherein the thread portion is induction tempered after tempering of the head portion and the shank portion.

### Claim 10 (depends on 9)

The fastening member of claim 9, wherein induction tempering of the thread portion includes heating the thread portion at a third pre-set temperature value for a pre-defined time period.

### Claim 11 (depends on 10)

The fastening member of claim 10, wherein the third pre-set temperature value lies between 400° C. and 600° C.

### Claim 12 (depends on 1)

The fastening member et claim 1 wherein the full shank portion length is between ½ and ¾ of a length of the body portion.

### Claim 13 (depends on 12)

The fastening member of claim 12 wherein the hardness value of the head portion and the shank portion is about 55 Rockwell C, and the hardness value of the thread portion is about 40 Rockwell C.