Method for setting shape and working stress, and working environment of steel member

• US 6,523,416 B2
• Filed: 08/29/2001
• Issued: 02/25/2003
• Est. Priority Date: 08/31/2000
• Status: Expired due to Fees

• Current Assignee: Kawasaki Steel Corporation (JFE Holdings Incorporated), National Institute for Materials Science
• Original Assignee: Kawasaki Steel Corporation (JFE Holdings Incorporated), National Institute for Materials Science
• Inventors: Takagi, Shusaku, Inoue, Tadanobu, Tsuzaki, Kaneaki
• Primary Examiner(s): Fuller, Benjamin R.
• Assistant Examiner(s): Martir, Lilybett
• Application Number:
  US09/940,669
• Publication Number:
  US 20020043111A1
• Time in Patent Office: 545 Days
• Field of Search: 737/60, 73/56, 737/63, 737/64, 73/74, 73/75, 73/76, 73/77, 73/190.7
• US Class Current: 73/760
• CPC Class Codes: C22C 38/04 containing manganese
• CPC Class Codes: C22C 38/22 with molybdenum or tungsten
• CPC Class Codes: G01N 33/2022 Non-metallic constituents
• CPC Class Codes: G01N 33/2045 Defects

Abstract

A delayed fracture is effectively prevented by appropriately setting a shape and working stress, and working environment of a high strength member having more than 1,000 MPa of tensile strength. For this end, the relationship between a maximum value of diffusible hydrogen contents of unfailed specimens (H_c) and Weibull stress are found and the content of diffusible hydrogen entered into steel from the environment due to corrosion during the use of the steel member (H_e) is also found. Then, Weibull stress in the H_c that is equal to the H_e is found, thus determining the shape and working stress of the steel member so as to provide stress below the Weibull stress.

Claims

1. A method for setting a shape and working stress of a steel member comprising the steps of:

determining the relationship between a maximum content H_c among diffusible hydrogen contents of unfailed steel specimens and Weibull stress;

measuring an environment content H_e of diffusible hydrogen penetrating the steel member from the environment;

determining the Weibull stress σ

_wA when H_c=H_e; and

determining the shape and working stress of the steel member when the Weibull stress σ

_wB in actual use is below the Weibull stress σ

_wA.

2. The method according to claim 1, wherein the Weibull stress is calculated by an electronic arithmetic unit in accordance with a finite element method based on the following Formula 1:

$\begin{array}{cc}{\mathrm{\sigma <br><br>}}_w={\left[\frac{1}{V_0<br><br>\text{\hspace{1em}<br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\int <br><br>}_{V_f}^{\text{\hspace{1em}<br><br>}}<br><br>{\left({\mathrm{\sigma <br><br>}}_{\mathrm{eff}}\right)}^m<br><br>\text{\hspace{1em}<br><br>}<br><br><br><br>V_f\right]}^{\frac{1}{m}}& \text{Formula <br><br> <br><br>1}\end{array}$

wherein σ

_eff is maximum principal stress which influences a fracture;

V_o is a reference volume of a certain area where a fracture is likely to occur;

V_f is an area where a fracture is likely to occur; and

m is a constant called Weibull shape parameter.

3. A method for setting a working environment of a steel member comprising the steps of:

determining the relationship between a maximum content H_c among diffusible hydrogen contents of unfailed steel specimens and Weibull stress σ

_wA;

determining Weibull stress σ

_wB of the steel member in actual use based on a shape and working stress of the steel member in actual use;

determining H_c when σ

_wA=σ

_wB; and

determining a working environment of the steel member when a content of diffusible hydrogen penetrating the steel member from the environment H_e is below the H_c.

4. The method according to claim 3, wherein the Weibull stress is calculated by an electronic arithmetic unit in accordance with a finite element method based on the following Formula 1:

$\begin{array}{cc}{\mathrm{\sigma <br><br>}}_w={\left[\frac{1}{V_0<br><br>\text{\hspace{1em}<br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\int <br><br>}_{V_f}^{\text{\hspace{1em}<br><br>}}<br><br>{\left({\mathrm{\sigma <br><br>}}_{\mathrm{eff}}\right)}^m<br><br>\text{\hspace{1em}<br><br>}<br><br><br><br>V_f\right]}^{\frac{1}{m}}& \text{Formula <br><br> <br><br>1}\end{array}$

wherein σ

_eff is maximum principal stress which influences a fracture;

V_o is a reference volume of a certain area where a fracture is likely to occur;

V_f is an area where a fracture is likely to occur; and

m is a constant called Weibull shape parameter.

5. A method for setting a shape and working stress of a steel member comprising the steps of:

determining the relationship between a maximum content H_c among diffusible hydrogen contents of unfailed steel specimens and Weibull stress σ

_wA;

measuring an environment content H_e of diffusible hydrogen penetrating the steel member from the environment;

determining the Weibull stress σ

_wA when H_c=H_e; and

comparing the σ

_wA to the Weibull stress σ

_wB which is calculated from a shape and working stress of the steel member in use, and determining that there will be no delayed fracture when the σ

_wA is larger than the σ

_wB.